The invention herein relates to a method of achieving full cure of a peroxide cured polyester resin. More particularly it relates to a method of effecting such curing in the presence of rubber.
In the manufacture of peroxide cured polyester resin articles it is often necessary to effect the curing of the resin in the immediate presence of rubber surfaces. A notable example of this situation occurs in the manufacture of fiber reinforced polyester pipe couplings which are to be cured while simultaneously molding a rubber gasket into the pipe wall. In the past this has been beset with significant difficulties, for it is commonly found that the polyester resin will not fully cure in the presence of the rubber, and the resin remains tacky in the area of the rubber/resin interface. The insufficient curing thus leaves the resin article badly weakened in the area of the interface and also prevents the rubber body from being properly retained by and/or adhered to the resin body. In the aforesaid pipe coupling, for example, such insufficient curing of the resin creates a weakened area in the pipe coupling wall and also prevents the rubber gasket from being satisfactorily retained within the structure, particularly when forces are exerted against the rubber gasket during joining of adjacent lengths of pipe in the field using such couplings. In addition, the uncured resin itself acts as a lubricant and allows the rubber gasket to be easily pulled out of the coupling.
In the past there have been attempts to devise elaborate mechanical structures to aid in retention of the rubber in position adjacent to the resin body. Gaskets have been designed, for instance, with elaborately ridged, dovetailed or otherwise configured external surfaces in attempts to form a mechanical interlock with the resin body after curing. Because the problem of incomplete cure is not dealt with directly, however, these mechanical expediences have been of only limited effectiveness. In addition, the complex structures have significantly raised the cost of the rubber articles (such as gaskets) because of the complicated rubber molding techniques required to form the complex surface configurations.
It would therefore be highly desirable to have a method for fully curing polyester resin in the presence of rubber, such that rubber bodies may be satisfactorily molded into and/or adhered to polyester resin bodies.